told us that bill was dealing with a lot of shady people, gun dealers. >> reporter: and that was one theory. but there was something else, too, or, rather, someone else. >> the only person that we knew was frustrated with him was his business partner who he was in the lawsuit with. >> reporter: all of them, bill's kids and nanette, told detective voth about that business partner, hal fischel. >> because he and mr. mclaughlin were in a heated multiyear lawsuit over the invention of the device. >> reporter: the device? bill had made his millions from a revolutionary medical invention, a machine that separates plasma from blood. it's still in use worldwide today. just the sort of thing bill wanted, to do something useful, helpful, and make lots of money, too. >> reporter: he enjoyed learning now things, discovering new things, and especially if it helped people, benefitted people, if he could make money off of an idea. >> reporter: hal fischel had worked with bill on an early phase of the machine. it was after fischel left the company that the money came rolling in. fischel thought his